ADB light distribution control has been proposed as one technique for producing a light distribution for preventing dazzling of the driver etc. of a vehicle(s) (hereinafter referred to “vehicle(s) ahead”) located in a region ahead of the self vehicle, such as a forward vehicle running in the same direction or an oncoming vehicle, while enhancing the effect of illumination of the region ahead of the self vehicle. In the ADB light distribution control, a vehicle ahead is detected by a vehicle position detecting device and a control is performed to reduce (to zero if necessary) the light quantity in a region where the detected vehicle ahead exists and illuminate the other wide regions brightly. In recent years, ADB light distribution control has come to be applied to headlamps having such light-emitting elements as LEDs as light sources. In the ADB light distribution control using LEDs, a light distribution for illuminating a region ahead of the self vehicle brightly is formed by combining respective illumination regions of plural LEDs as light sources and, if a vehicle ahead is detected, the light quantity is reduced (to zero if necessary) in illumination regions corresponding to the detected vehicle ahead. In the following description, reducing the light quantity of illumination regions will be referred to as “light quantity reduction” in a sense that it includes reduction to zero.
In the above-described ADB light distribution control, if there occurs a deviation between a position of a vehicle ahead detected by the vehicle position detecting device and actual illumination regions in which the headlamp light quantity is reduced, the vehicle ahead may be illuminated with light to dazzling its driver etc. Or the light quantity may be reduced in an unnecessarily large region to lower the visibility of a region ahead. In particular, systems that perform an ADB light distribution control are associated with various kinds of errors such as an attachment position error of the vehicle position detecting device for detecting a vehicle ahead, a calculation error occurring in detecting a vehicle position by the vehicle position detecting device, and an illumination region setting error that is associated with an error of setting of the lamp optical axis of the headlamp. This makes it difficult to completely eliminate the deviation between a detected position of a vehicle ahead and illumination regions of the headlamp. To solve this problem, Patent document 1 proposes a technique that prevents dazzling of the driver etc. of a vehicle ahead that is caused by an error between a detected position of a vehicle ahead and illumination regions by setting detection margins for detection of a vehicle ahead and giving redundancy to a detection output using the detection margins.
In Patent document 2, plural LEDs are arranged as light sources in each of left and right headlamps. Each headlamp forms plural illumination regions arranged in the horizontal direction (left-right direction) by means of the plural LEDs, and a prescribed light distribution pattern is formed by these plural illumination regions combined. When a vehicle ahead has been detected, in each headlamp LEDs to be lit or not to be lit are changed according to a movement of the vehicle ahead. In this manner, even if a vehicle ahead is moving, illumination regions where the vehicle ahead exists is rendered in a non-illuminated state to prevent dazzling of the driver etc. of the vehicle ahead. On the other hand, regions where the vehicle ahead does not exist is illuminated to increase the visibility of a region ahead of the self vehicle.
In vehicles, in particular, automobiles, that employ ADB light distribution control, in many cases the vehicle position detecting device is installed at the center in the width direction of the vehicle body of the automobile whereas the left and right headlamps are disposed at front-left and front-right positions of the automobile. Therefore, there exists an angular deviation called a parallax angle between an angle (hereinafter referred to as a “detection angle”) that is formed when a vehicle ahead is viewed from the vehicle position detecting device and an angle (hereinafter referred to as an “illumination angle”) of the lamp optical axis of illumination of a vehicle ahead with illumination light emitted from the left or right headlamp. Because of the presence of the parallax angle, even if a vehicle ahead is detected with high accuracy, light quantity reduction regions of the left and right headlamps cannot be positioned correctly with respect to the vehicle ahead, possibly resulting in dazzling of the driver etc. of the vehicle ahead. To prevent dazzling of the driver etc. of a vehicle ahead due to this angular deviation, Patent document 3 proposes a technique that controls the illumination angles of the left and right headlamps by calculating a parallax angle on the basis of a distance to a vehicle ahead (intervehicle distance) and a vehicle width and corrects a detected angle for the parallax angle.